JP3003964B2 - Measurement interferometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a length measuring interferometer.

[0002]

2. Description of the Related Art Conventionally, various types of interferometers for length measurement have been proposed. The most basic configuration is
There is a Michelson interferometer that detects an interference fringe (fringe) for every half wavelength and measures the moving distance by counting the number of fringes.

Further, S.M. J. There is a so-called double-pass interferometer proposed by Bennett. This is 1
Since the fringe corresponds to a quarter wavelength, the sensitivity can be doubled as compared with the above-mentioned Michelson interferometer. (S.
J. Bennett Optics Comics
ation, vol. 4 (1972))

The Bennett interferometer will be described with reference to FIG. Incident light 1 includes a two polarization components (the linearly polarized light component vibrating in the direction perpendicular to each other within a plane perpendicular to the traveling direction of light), now a polarization component oscillating in a plane including the incident direction by the solid line 1a, and a polarized light component that vibrates orthogonally thereto is indicated by a broken line and described as 1b. The polarized component 1a transmits through the polarizing film 4 of the polarizing prism 3, passes through the quarter-wave plate 6, is reflected by the movable mirror 7, and is again reflected by the quarter-wave plate 6.
And returns to the polarizing prism 3. Since the polarized light component 1a has passed through the quarter-wave plate 6 twice, the oscillating plane has been rotated by 90 °, so it is reflected by the polarizing film 4 of the polarizing prism 3 to the corner cube 19, where it is reflected and polarized. The light is reflected by the polarizing film 4 of the prism 3, passes through the quarter-wave plate 6 again, hits the moving mirror 7, and returns to the polarizing prism 3 through the quarter-wave plate 6. Here since polarization component 1a was further passed through the quarter wave plate 6 twice, because the vibration surface is rotated 90 °, this time fringe detection unit (not shown) as measuring light 1 0 a is transmitted through the polarization prism 3 Head for.

On the other hand, a polarization component 1b (shown by a broken line) of a vibration component orthogonal to the polarization component 1a has a direction of a vibration plane different from that of the polarization component 1a by 90 °. relationship is opposite of the polarized light component 1a, along a path shown in broken line towards the interference fringe detector as reference light 1 0 b, the interference fringes where by causing interference between polarization components 1 0 a, 1 0 b Can be done.

Now, the path shown by a solid line is called a measurement optical path, and the path shown by a broken line is called a reference optical path. When the movable mirror 7 moves right and left in the figure so as to approach or move away from the polarizing prism 3, the interference fringes move because the difference between the reference optical path length and the measurement optical path length changes. By counting the number of these stripes, the movement distance of the moving stripe (the length between the original position and the moved position) can be determined, and the length can be measured.

[0007]

However, in such a conventional interferometer, the effective diameter of a split optical element such as a semi-transparent mirror or a polarizing prism for splitting light from a light source into measurement light and reference light is as follows. It is necessary to make it larger than the diameter of the measurement beam. Therefore, if an attempt is made to increase the diameter of the measurement beam, the size of the optical element itself increases, and the size of the entire apparatus increases, so that the cost must be increased. Further, even in a double-pass interferometer as shown in FIG. 6, if an attempt is made to increase the measurement beam diameter or the beam interval, the problem that the effective diameter of the polarizing prism 3 and the corner cube 19 must be increased is not solved.

The present invention solves the above-mentioned problems, and in the double-pass interferometer, it is possible to reduce the diameter of the measuring beam and the diameter of the polarizing prism as compared with the beam interval, and it is not necessary to use a corner cube. An object of the present invention is to provide an interferometer having a configuration.

[0009]

Means for Solving the Problems To achieve the above object,
Therefore, the length measuring interferometer according to the present invention focuses the parallel light beam and
The first method of obliquely entering the split optical elementFocusing means
When,SaidTransmitted and reflected by split optical element
The second and third light beams are converted into parallel light beams, respectively.Focusing means
When,TheSecond and third light collecting meansBehindPlaced in1/4
A wave plate;1/4To the optical axis of the collimated light beam emitted from the wave plate
Fixed and movable reflecting mirrors located vertically with respect to the reflecting mirror
The parallel light beam reflected by thePrevious
RecordSecond, thirdFocusing meansTo make a convergent light,
A reflecting mirror is provided at the convergence point of the converging light, and the reflecting mirror andSaidSecond,
ThirdFocusing meansAnd make up the cat's eye
And thatIs what you do. In addition, the measurement according to the present invention
The long interferometer isThe split optical element and the second and thirdCollection
Light meansWith two hemispherical lenses whose focal length is equal to their diameter
Is replaced with a spherically formed optical element via a polarizing film.
Is characterized byare doing.

[0010]

As described above, the convergent light is obliquely incident on the splitting optical element, and the splitting optical element is used in the portion where the converged light flux is most concentrated. The beam interval between the reference beams can be set arbitrarily wide regardless of the effective diameter of the split optical element. Each of the measurement light and the reference light emitted from the splitting optical element is a divergent light, and the lens for converting the light into a parallel light constitutes a catseye and a reflecting mirror provided at the converging position of the parallel light at the same time. Alignment of the optical system is facilitated even without using.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a length measuring interferometer according to the present invention will be described below in detail with reference to FIG. A parallel light beam 1 of linearly polarized light from a light source (not shown) is converged by a lens 2 and obliquely enters a split optical element (a semi-transmissive mirror or a split optical element, but a polarizing prism is used here) 3. Here, the polarizing prism 3 is disposed such that one end face 3 a of the polarizing prism 3 is located at the focal position of the lens 2. One of the light beams is a polarizing film 4
Is transmitted by the lens 5, becomes a parallel light beam by the lens 5, passes through the 波長 wavelength plate 6, becomes circularly polarized light, and is reflected by the movable reflecting mirror 7. The reflected light is again converted into linearly polarized light via the quarter-wave plate 6, but at this time, since the polarization plane is rotated by 90 °, the reflected light is reflected by the polarizing film 4. This light beam is convergent light, and another end face 3b of the polarizing prism 3 is located at the converging position. If the reflecting mirror 8 is formed on the end face 3b by vapor deposition or the like, the light reflected by the reflecting mirror 8 is again reflected on the polarizing film 4.
, And becomes parallel light at the lens 5, passes through the 波長 wavelength plate 6, and travels to the movable reflecting mirror 7. Here, the lens 5 and the reflecting mirror 8 constitute a cat's eye. The light beam reflected by the movable reflecting mirror 7 passes through the polarizing film 4 and becomes a parallel light 10 by a lens 9, and travels to an interference fringe detecting unit (not shown). This parallel light flux 10 is used as measurement light.

On the other hand, the light beam 1 incident from the lens 2 and reflected by the polarizing film 4 becomes parallel light by the lens 11, passes through the quarter-wave plate 12, is reflected by the fixed reference mirror 13, and is reflected by the polarizing film. Then, the light passes through the mirror 4 and is focused on the reflecting mirror 8 formed on the end face of the polarizing prism 3. The light reflected by the reflecting mirror 8 is applied to the polarizing film 4.
Through the lens 11, the quarter-wave plate 12, and reflected by the reference mirror 13. Here, the lens 5 and the reflecting mirror 8
As in the case of (1), the lens 11 and the reflecting mirror 8 constitute a cat's eye. Light reflected by the reference mirror 13 is reflected by the polarizing film 4 and becomes parallel by the lens 9. When this parallel light beam is used as the reference light, it interferes with the above-described measurement light, and the interference fringe detecting unit can detect the interference fringe.

FIG. 2 shows a second embodiment of the present invention. In place of the two lenses 2 and 9 in FIG.
In this case, the number of lenses 14 is used. In this case, the number of lenses can be reduced.

FIG. 3 shows a third embodiment of the present invention, in which the position of the reflecting mirror 8 in FIG.
End faces away from the 3 b of, it is obtained by a reflecting mirror 15. In this case, since the distance between the reflecting surface of the reflecting mirror 15 and the polarizing film 4 of the polarizing prism 3 is increased, the angle at which the light beam enters the polarizing film 4 can be reduced.

FIG. 4 shows a fourth embodiment of the present invention.
a and 16b. In the figure, the hemispherical lenses 16a and 16b are formed in a spherical shape via a polarizing film 17, and their respective focal lengths are equal to the diameter of the hemisphere. Further, a concave reflecting mirror 18 is provided on the outer periphery of the hemispherical lens 16b. Therefore, the hemispherical lenses 16a and 16b fulfill the functions of the polarizing prism 3 and the lenses 5 and 11 in the first embodiment, and these optical elements can be omitted, and a compact interferometer can be provided. . Besides, two hemispherical lenses 1
If the light beams 6a and 16b are configured to be rotatable so that the angle of the light beam incident on the polarizing film 4 can be changed, it is extremely necessary to adjust the light beam to enter the movable mirror 7 and the reference mirror 13 vertically. This facilitates optical alignment.

FIG. 5 shows a modification of the fourth embodiment. That is, in the fourth embodiment, the light beam passes above and below the polarizing film 17, but in this embodiment, the angle at which the light beam enters the polarizing film 17 differs between the upper and lower directions. The percentage of intensity will be different. Therefore, as shown in FIG. 5, there is an advantage that the angle of the incident light beam can be made the same by making the incident light beam pass right and left of the polarizing film 17.

[0017]

According to the present invention, the convergent light is made to be obliquely incident on the length measuring interferometer, so that the size of the splitting optical element such as the polarizing prism can be reduced and the corner cube is used. Even without this, optical alignment becomes easy. In addition, a new effect is expected in that the beam intervals of the measurement light and the reference light can be arbitrarily set irrespective of the effective diameter of the prism, and a compact and low-cost double-path type interferometer for length measurement can be provided. .

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of a length measuring interferometer according to the present invention.

FIG. 2 is a schematic configuration diagram showing a second embodiment of the length measuring interferometer according to the present invention.

FIG. 3 is a schematic configuration diagram showing a third embodiment of the length measuring interferometer according to the present invention.

FIG. 4 is a schematic configuration diagram showing a fourth embodiment of the length measuring interferometer according to the present invention.

FIG. 5 is a schematic configuration diagram showing a modification of the fourth embodiment.

FIG. 6 is a schematic configuration diagram showing a conventional example of a length measuring interferometer.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 parallel light from light source 2 lens 3 split optical element (polarizing prism) 4 polarizing film 5 lens 6 1/4 wavelength plate 7 moving mirror 8 reflecting mirror 9 lens 10 parallel light 11 lens 12 1/4 wavelength plate 13 reference mirror 14 Lens 15 Reflecting mirror 16a Hemispherical lens 16b Hemispherical lens 17 Polarizing film 18 Reflecting mirror 19 Corner cube

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01B 9/00-11/30 102

Claims (2)

(57) [Claims] 1. A a first condensing means allowed to obliquely incident to splitting optical element condenses the parallel light beam to the respective parallel light beams divided transmitted and reflected divergent light by the splitting optical element second, a third condensing means, the second, and a quarter-wave plate disposed behind the third focusing means, the optical axis of the parallel light beam emitted the quarter-wave plate and the fixed and movable reflectors located vertically again collimated light flux reflected by the reflecting mirror, the quarter-wave plate, and the second, convergent light passed through the third condensing means, said convergence a reflecting mirror provided on the converging point of light, the reflecting mirror and front
A cath's eye is constituted by the second and third condensing means , respectively. Wherein said splitting optical element and the second, third condensing
Light means, characterized by being replaced with an optical element obtained by forming a spherical two hemispheres focal length equal to its diameter lens through the polarizing film, the interference length measuring according to claim 1 Total.